Bleaching compositions, i.e., compositions containing a peroxygen bleaching compound as well as compositions containing bleach activators to help oxygen release at all temperatures, are well known in the art. U.S. Pat. No. 4,412,934 to Chung et al., for example, teaches bleaching compositions providing effective and efficient surface bleaching over a wide range of bleach solution temperatures. U.S. Pat. No. 5,047,163 to Batal et al. teaches a specific class of activators (also known as bleach precursors) used in bleaching compositions.
One major drawback with all compositions comprising peroxygen bleach compounds is that these compositions can cause damage to fabric such as dye damage and/or loss of textile strength of fabric fibers. The damage appears to be worse in the presence of transition metal ions such as copper, iron, manganese or chromium. Such metals are often naturally found in water or as minor contaminants in the ingredients which comprise the bleaching formulations. They may also come from food stains. Without wishing to be bound by theory, it is believed that the peroxygen bleach compounds themselves may be responsible for dye and fabric damage, and further that the metal ions noted above may catalyze the decomposition of peroxygen bleaches to form highly reactive radical species that are responsible for such damage.
In one embodiment of the invention, applicants have now found that a class of radical scavengers, known as nitrones, significantly reduce dye and fabric damage caused by peroxygen bleach compounds, particularly those found in compositions comprising the transition metals noted above. Again, without wishing to be bound by theory, it is believed that the nitrones react with radical species to form secondary radicals that are less reactive by nature. Less reactive radicals will in turn result in less dye and fabric damage.
In a second embodiment of the invention, another class of scavengers, known as nitroso spin traps, also reduce dye and fabric damage caused by peroxygen bleach compounds, especially those containing transition metals as noted above.
Chinese Patent No. 1,095,756 describes the use of "nitrones" in liquid detergent for removal of thick grease and collected carbon on mechanical parts; and for use on ceramics, plastics and other ware. There is no teaching of nitrones in a bleach containing liquid formulation, let alone any teaching or suggestions that nitrones could react with radicals produced from peroxygen bleach compounds to prevent dye or fabric damage.
U.S. Pat. No. 5,723,502 to Peter Proctor describe nitrone and nitrone spin traps and a method for treating hair loss. There is no teaching or suggestion of use of these compounds in bleach liquid formulations.